The goal of this Core is to create whole-heart models of normal and failing rabbit hearts from Diffusion Tensor Magnetic Resonance Imaging (DTMRI), to serve as a platform for whole-heart model testing of the hypotheses developed by the Projects. Our basic strategy is to take the phenomena being studied in the Projects, and place them into anatomically accurate whole-heart models to ask the critical question: how do these molecular, cellular, and tissue-level effects play out in the anatomically complex failing heart? In order to create these models, we have developed new mathematical methods for creating structural models from DTMRI. The review endorsed the idea that whole heart modeling is a useful strategy. It also endorsed our new methods for creating high-resolution detailed geometric models of particular hearts, using DTMRI raw data. Due to the new restrictions on proposal length, we are omitting a lot of the detailed technical presentation of these methods from the previous proposal. The review also supported our third aim, which is to provide quantitative data analysis tools for the Projects. ("... quantitative data analysis, which is highly important for drawing the correct conclusions from the experimental data.... The ideas related to the interpretation of optical recordings of transmembrane voltage activity are interesting and important) The review of the links to the Projects commented: "...Links to 1 [and] Link to 3 is strong, 2 and 4 less so." In response, we have strengthened the interactions with Projects 2 and 4.